TCP/IP not handling "DUP ACK" from the remote end

[watsonads]

I'm evaluating the performance of the hardened tcp/ip stack with the iperf client user module. After transferring for less than 1sec, the transfer stop. I monitor the tcp traffic with wireshark. I can find a lot of "DUP ACK" packet from the iperf server side (Desktop PC with 100G QSFP interface).

The DUP ACK packets all point to the same sequence number - 872278593.

Looks like tcp/ip not response to "DUP ACK".
Please advise.

Watson